Replicating natural topography on marine artificial structures:A novel approach to eco-engineering

Ocean sprawl is a growing threat to marine and coastal ecosystems globally, with wide-ranging consequences for natural habitats and species. Artificial structures built in the marine environment often support less diverse communities than natural rocky marine habitats because of low topographic complexity. Some structures can be eco-engineered to increase their complexity and promote biodiversity. Tried-and-tested eco-engineering approaches include building-in habitat designs to mimic features of natural reef topography that are important for biodiversity. Most designs mimic discrete microhabitat features like crevices or holes and are geometrically-simplified. Here we propose that directly replicating the full fingerprint of natural reef topography in habitat designs makes a novel addition to the growing toolkit of eco-engineering options. We developed a five-step process for designing natural topography-based eco-engineering interventions for marine artificial structures. Given that topography is highly spatially variable in rocky reef habitats, our targeted approach seeks to identify and replicate the ‘best’ types of reef topography to satisfy specific eco-engineering objectives. We demonstrate and evaluate the process by designing three natural topography-based habitat units for intertidal structures, each targeting one of three hypothetical eco-engineering objectives. The process described can be adapted and applied according to user-specific priorities. Expanding the toolkit for eco-engineering marine structures is crucial to enable ecologically-informed designs that maximise biodiversity benefits from burgeoning ocean sprawl

Artificial shorelines lack natural structural complexity across scales

From microbes to humans, habitat structural complexity plays a direct role in the provision of physical living space and increased complexity supports higher biodiversity and ecosystem functioning across biomes. Natural coastlines are structurally complex transition zones between land and sea that support diverse ecological communities but are under increasing pressure from human activity. Coastal development and the construction of artificial shorelines are changing our landscape and altering biodiversity patterns as humans seek both socio-economic benefits and protection from coastal storms, flooding, and erosion. In this study, we evaluate how much structural complexity is missing, and at which scales, with the creation of artificial structures compared to naturally occurring rocky shores. We quantified the structural complexity of both artificial and natural shores at resolutions from 1 mm through to 10s of m using three remote sensing platforms (handheld camera, terrestrial laser scanner and uncrewed aerial vehicles) across both artificial and natural shorelines. Natural shorelines were approximately 20-50 % more structurally complex and offered greater structural variation between locations. In contrast, artificial shorelines were more structurally homogenous and typically deficient in structural complexity across scales. Our findings reinforce concerns that replacing natural rocky shorelines with artificial structures simplifies coastlines at organism-relevant scales. Furthermore, we offer much-needed insight into how structures might be modified to more closely capture the complexity of natural shorelines that support biodiversity